1. Field of the Invention
This invention relates to an upper feed dog automatic regulator for an overlock machine, more particularly, to an apparatus for the overlock machine having such mechanisms that the lowest limit of an elliptical locus drawn by the upper feed dog is predetermined to meet cloth to be sewn but the lowest limit is adjustable automatically according to the change of thickness of upper and lower cloths due to a stepped part, a protruding part, etc. The lengthwise feed of the feed dog is adjustable easily by moving a lever on an indicator. The upper feed dog is adjustable in height according to the thickness of cloth to be sewn. Both the presser foot and the feed dog can be lifted up by pedalling. The upper feed dog is divided into a front part and the rear part, as in a case of the lower feed dog, so that the lengthwise feed and lifting feed of both feed dogs are differentiated by a differential feeder. With such arrangement, uneven material feed puckering between the front and near upper feed dogs and other troubles can be prevented also, material cloth of different kind can be sewn together with a good result.
2. Description of the Prior Art
In the conventional overlock machine of this kind, the upper feed dog which moves along an elliptical locus in contact with the upper surface of an upper cloth is provided opposite to the lower feed dog for the purpose of preventing uneven material feeding and other sewing troubles. This arrangement causes no trouble in sewing a plain portion of cloth but has such disadvantage in the case where a stepped part, a protruding part, or the like exists in upper and lower cloths. While both the lower feed dog and the upper feed dog are moving along the respective elliptical locus, the distance between the least upper bound and the greatest lower bound for a plain portion causes partially an abnormal pressure on the cloth, with the result of causing a bad sewing effect.